The first question many site designers and business owners ask when confronted with accessibility requirements is "Why?". That's a reasonable question to ask, and an easy question to answer. The reason is simple. There is a significant portion of the population with disabilities. According to The Center for an Accessible Society there are over 49 million Americans living with a disability of some type, with over 30 million between the ages of 21 and 64. That's nearly 20% of the population or 1 out of every 5 people.

Even with nearly 20% of the population having some type of disability, many corporate web sites simply ignore some of the most basic accessibility guidelines.

Many companies and web site owners do not fully appreciate the impact of making a site non-accessible. Imagine if your local WalMart or Target store had a greeter that told every fifth person to leave because they didn't want to make their store accessible. That store would be in big trouble, not just legally, but financially as well.

One of the most common defenses against making a site accessible is that it is either too costly to do, or it is to complex to adhere to the guidelines.

The former of these arguments is difficult to justify because simply saying "no thanks, we don't want to help you" to up to 20% of your visitors can't be good for the bottom line.

The later, that the regulations and guidelines are too complex, in my opinion, cannot be justified. Although there are many guidelines, they are no more complex than the basic rules of HTML coding. Simple items such as proper use of alt tags, using semantic HTML, and ensuring content can be accessed without the use of javascript, flash or another proprietary plug in are fairly basic things to implement, and go a long way towards making your site more accessible.

To summarize, accessibility matters because it makes for a better user experiences for ALL visitors to your web site, and because if makes business sense.

I disagree here. I mean seriously 20% of websurfers cannot be inaccessible. I would go on to argue that there are not even 10% that cannot access these websites. If they are blind I mean really, I don't think they have much interest in the internet... If they just have troubles seeing there are different options with windows to make things bigger. Honestly it may also depend on your site. Like I mean a gaming site for halo or something, wouldn't need to be accessible. Anyways other than me being a little iffy on the facts you gave me I'm not to sure I will be making any great effort into making my site perfect for blind, and or bad site viewers. 20%?!?!?! I don't think even 20% of America is non-accessible to the internet.

One thing to keep in mind when you're talking about accessibility is that it does not mean a specific disability. There are very VERY common disabilities such as color blindness that effect anywhere between 12% and 20% of the population. Color blindness is probably the single most overlooked accessibility checkpoint.

Add to that a few percent of the population with physical disabilities, legal blindness, and other disabilities and I'm sure you'll realize that 20% of the population does, in fact, have a disability that can potentially stop them from accessing content on a site.

Making a site accessible means that everyone, regardless of device they're using, will be able to access the content. Making a site with a red-green or yellow-blue (the most common color blindness types) color scheme makes them dependent on a device that can read the screen content, or other device because they may not be able to read the content themselves.